Superheterodyne receiver



Aug. 28, 1928.

F. B. FALKNOR v SUPERHETERODYNE RECEIVER Filed Dec. 29, 1923 R o T N E V m M n M E B M m ATTORNEY Patented Aug. 2a, 1928.

UNITED STATES PATENT OFFICE.

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Application Med December 88, 1988. serial No. 888,856.

This invention relates to systems for. receiving, amplifying and translating radio signals. It is particularly related to devices known as super-heterodyne receiving systems, which are exemplified by the patent to Armstrong 1,342,885, for a method of receivlng high frequency oscillations.

It is an object of this invention to produce an amplifier, of the type stated, WhlCh. shall require fewer vacuum tubes and fewer ad ustments than amplifiers of this type have heretofore em loyed.

It is a urther object of this inventlon to produce an audio-frequency modulation in the output of the generator which forms part of the heterodyning device. This gives a double-frequency characteristic to the energy in the input of the first rectifier, which requires two rectifiers working in tandem for converting the signal into a form of energy to which the telephones can-respond.

Associating the means for producmg audio frequency with the same tube that generates the current used for heterodyning enables one tube to serve two purposes, and the consequent reduction in the cost of the apparatus is accompanied by a greater simpllclty. Tuning is also rendered easier because, at least 1n one form of the invention, there are fewer c1rcuits to tune. Other objects of the invention and details of the construction used will be ap arent from the following descri tion and t e accompanying drawings in w ich,

Figure 1 is a diagram of. one form of the invention and Fig. 2 is a diagram of another form.

The receiving system includes an antenna 1 which has the usual tuning condenser 2, 1nductor 3, and ground connection 4. Coupled to the antenna circuit by the inductor 3, 1s a generator, including a vacuum tube 5, the plate circuit of which includes a coil (Send the gridcircuit a coil 7, both of which form niembers' of the coupling. The inductor 7 is in parallel with an adjustable condenser 8, by means of which the frequency of the oscillations produced by the generator is controlled. This frequency 18 so selected that it diflers from the frequency of the incoming signals. The difference gives rise to beats.

The output of the heterodyne, that is, the combined effect of the signahng current and granted June 8, 1920, .h

the current generated by the tube 5, is received upon the gr d of a tube 9. A 11 and a gr d-leak condenser 12 enable this tube to act as a detector. The detector receives energy from both the antenna and the eterodyne generator. The output of this detector, therefore, carries a current having the frequency of the beats. The antenna circult is tuned, by means of the condenser 2, to

the frequency of the incoming signals. The

condenser 8 controls the frequenc impressed upon the inductor 3 by the hetero yne generator. The difference between this and the frequency of the incoming signals determines thefrequency of the beats and so the freqofency in the output from the tube 9.

This at frequency isabove and, preferably, only slightly above, audio-frequency. The incoming signals areof a frequency so high that they cannot readily be am lified, but the beat fr uency may be amplified without dlificulty. n the other hand, because the beat fr uenoy is above the limit of audition,

grid condenser frequency any ten ency of the tube 9 to oscillate will not produce noises in the telephones.

The output circuit of the tube 9 is coupled, by means of a transformer 13, to an amplifier including the tube 14. The secondary of the transformer 13 is tuned, by a condenser in parallel therewith, to the beat fr uency. Consequently, neither the frequency de ivered by the tube 5, unaccompanied by the signaling frequency, nor the signaling frequency.

alone can reach the tube 14 in any substantial amount, for both of these differ widely from the beat frequency.

The tube 14, in its turn, is coupled by means of a tuned transformer 15 to a tube 16. The grid connection of the tube 16 includes a condenser 17 and a grid-leak resistance 18,

which will enable the tube 16 to act as a detector for radio frequencies. The output of the tube 16 contains the telephone receiver 19, shunted, in the usual way, by a fixed condenser 21. The filaments in the several tubes are heated by a common filament battery 22, and the plate circuits are fed by a common battery 23.

An audio-frequency variation in the output of the tube9 would be present if the incoming signals were modulated at an audio frequency. If this were the case, no structure, in addition to that already described, need be employed. Such an arrangement would all be well adapted to the reception of telephonic signals. The present invention, in order to provide for the reception of telegraphic signals, produces an audio-frequency variation by local means. In Fig. 1 this is done by means of a buzzer 24,wh1ch is energized from the batte 22 and intermittently closes the grid circuit of the heterodyne generator 5 at the contacts 25. The frequency of the interruptions by the buzzer is withm the limit of audibility and so produces a note in the telephone 19 whenever the signaling energy is present on the antenna. When no signa ing energy is arriving, thebuzzer produces interruptions in the output of the generator 5, but, the frequency of this generator being far above the frequency to whlch the transformer 13 is tuned, under these conditions, no energy is transferred to the tube 14.

In the form shown in Figure 2, instead of a buzzer for the modulation of the output of the heterodyne generator, an oscillating circuit tuned to audio frequency is used. This circuit includes the secondary 26 of an audio-frequency transformer 30 and a condenser 27 in parallel with the secondary. For the sake of effectively transmitting energy from the battery 23 to the oscillation circuit just described, the primary 28 of the transformer has a condenser in parallel therewith, which provides a second oscillating circuit that is also tuned to the same frequency. This primary circuit is in the plate connection of the vacuum tube 5., but the secondary and its condenser are in the grid circuit of this tube.

The action of the tuned circuits, associated with the audio-frequency transformer 30, superposes an audio-frequency modulation upon the high frequency determined by the inductor 7 and condenser 8. Consequently, the energy impressed upon the antenna circuit at the inductor 3, consists of a current having beats and also a modulation. The detector 9, therefore, produces, in-the primary of the transformer 13, a current modulated at an audio frequency, and the frequency of the current corresponds to the beats. This is amplified by the tube 14 and transferred by the transformer 15 to the grid circuit of the tube 16. The tuning condenser in parallel with the secondary of transformer 15 adds to the selectivity of the system. This transformer delivers the beat frequency current to the detector tube 16 and the output of this tube will have a frequency corresponding to the modulation.

If there be no si aling energy in the antenna, the output 0 the generator 5 alone, instead of beats, is present in the receiving circuit or the input circuit of the detector tube 9 and the transformer 13 is not adapted to transmit such a bi h frequency; therefore, no note will be pr uced in the telephone 19 emept when signaling energy is present on ducing signals of radio frequency, a receiving apparatus, including a heterodyne generator and producing from said signals correspond ng signals of a frequency lower but above audibiht and means controlling the amplitude of t e output of said heterodyne generator for producing audio-frequency modulations of said lower-frequency signals.

2. In a radio receiving system, a reception circuit, a generator of sustained oscillations having a frequency differing from the freuency of the received signals by an amount t at will produce a beat of a lower frequency but above audibility, means for varying the amplitude of the output of said generator, said variations being at audio frequency, and means for impressing the varied output of the generator u on the reception circuit.

3. In a ra 'o signal-receiving system, means at the receiving station, including an oscillation generator and a detector, for producing a beat of a frequency below that of the signals and above audibility, means for modulatln the output of the generator at an aud1o equency, and a second detector ultimately controlled by the output of the first detector.

4. A radio receivin system, comprising two detectors, 9. hetero yne generator co-operating with the first detector to reduce a beat frequency in the output of sai detector, means for varying the output of said heterodyne (generator at an audio frequenc and a secon detector ultimately controll by the output of the first detector.

5. In a device for receiving radio signals a heterodyne generator having a vaeuum-tube device with a grid connection and a plate connection regeneratively coupled, an antenna circuit coupled to said two connections, means in the grid connection for determining the frequency of the generator, a detector connected to said antenna circuit, the difference between the frequency of said heterodyne generator and the frequency in said antenna circuit roducing in the out ut of said detector a requency above an ibility and low enough to be readily amplified, means for amplifying the output of said detector a second detector coupled to said amplifying means, an indicating device fed by said second detector, and modulating means of audio frequency in the grid circuit of said heterodyne generator, whereby audio-frequency modulations will be produced in the output of the first named detector, detected by said second detector, and translated by said indicatin' device. v

6. e method of amplifyin and receiving high-frequency electrica oscillatory energy which comprises combining the incoming energy wit locall generatedhi hfrequency continuous osci ations of m u-v lated amplitude of a fre uency differing from said incoming energy y a. third readilyamplifiable high frequency, the modulation being of audio frequency, converting the combined energy by suitable means to produce said readily-amplifiable high-frequency oscillations, am lifying the sad third hi h-frefrequenc quency'osci lations, and detecting an indicaiing the resultingamplified oscillations.

he method .of am lifyin and receiving high-frequency e ectrica oscillatory energy which comprises combining the incoming energy wit locally generated high continuous electricaloscillations of modu ated amplitude and of a. frequency differing from said incoming energy by a third readily-amplifiable high frequency, the modulation being ofaudio frequency, rectifying the combined energy to produce said 'readily-ampllifiable high-fr uency oscilla- 'fying the said t ird high-fre- 5 amp uenc oscillations and detectin and indicatin the resulting amplified oscillations.

8. he method of indirectly amplifying high-frequency electrical osciliatory energy which comprises combining said energy with high-frequency continuous electrical oscilla-' tions toproduce a third readily-amplifiable uency,-varying said continuous electrical prises generating energy of a frequency differing from the frequency of said signals by a third frequency, modulating the amplitude of said generated energy with an audio-frequency modulation, combining said generated and modulated energy with the signal energy,

rectifying the combined energy, amplifying the result, and detecting and indicating the output of said amplificationJ In testimony whereof, I have hereunto subthis 27th day of December,

scribed my name 1923;

FRANK B. FALRNOR. 

